The invention relates to adhesives for polycarbonate and surface-coated polycarbonate substrates.
Digital versatile discs are examples of articles that include two polycarbonate substrates bonded together through an adhesive composition. One or both of the polycarbonate discs may contain data. To enable the data to be read by an optical reader, at least one of the polycarbonate discs has a metal-coated surface, e.g., a 50 nm coating of aluminum. The second polycarbonate disc often has a coating of aluminum, gold, silicon oxide, or silicon carbide.
One problem in selecting a suitable adhesive composition for the discs is the potential for polycarbonate to outgas, which makes it difficult for many adhesives to maintain the integrity of an initially formed bond between the adhesive and the surfaces of the discs. If debonding (i.e., adhesive failure and/or cohesive failure) is present, it can be difficult or impossible for the optical reader to read the data. In addition, many adhesive compositions contain chemical species that corrode the metal coating. The rate of corrosion and debonding tends to increase as humidity and temperature increase.
In one aspect, the invention features an article that includes: a) a first polycarbonate substrate, b) a second polycarbonate substrate, and c) an adhesive composition disposed between the first polycarbonate substrate and the second polycarbonate substrate such that the first polycarbonate substrate is bonded to the second polycarbonate substrate through the adhesive composition. The adhesive composition includes an adhesive polymer that includes the reaction product of 1) an N-vinyl containing monomer selected from the group consisting of N-vinyl caprolactam, N-vinyl pyrrolidone, and N-vinyl imidazole, and combinations thereof, and 2) an acrylic acid ester monomer of a non-tertiary alcohol having an alkyl group comprising 4 to 20 carbon atoms. In some embodiments, the article is substantially free of debonding after being subjected to Accelerated Aging Test Method II.
In preferred embodiments, the article is substantially free of debonding after exposure to 90% relative humidity at 80xc2x0 C. for 16 hours. In other embodiments, the adhesive composition is substantially free of bubbles after the article is exposed to 90% relative humidity at 80xc2x0 C. for 16 hours.
In one embodiment, the article further includes an inorganic layer disposed on a surface of the first substrate and the adhesive composition is in contact with the inorganic layer. In some embodiments, the inorganic layer is a metal. Example of suitable metals include aluminum, silver, brass, gold, gold alloy, copper, copper-zinc alloy, copper-aluminum alloy, aluminum-molybdenum alloy, aluminum-tantalum alloy, aluminum-cobalt alloy, aluminum-chromium alloy, aluminum-titanium alloy, and aluminum-platinum alloy and combinations thereof. In some embodiments, the metal layer is reflective to light having a wavelength from 375 nm to 850 nm.
In another embodiment, the metal layer is substantially free of corrosion after the article is subjected to Accelerated Aging Test Method II. In a preferred embodiment, the metal layer is substantially free of corrosion after the article is exposed to 90% relative humidity at 80xc2x0 C. for 16 hours, most preferably the metal layer is substantially free of corrosion after the article is exposed to 90% relative humidity at 80xc2x0 C. for 1000 hours. In other embodiments, the metal layer is substantially free of corrosion after the article is exposed to 85% relative humidity at 80xc2x0 C. for 100 hours.
In some embodiments, the inorganic layer is semi-transparent. In other embodiments, the inorganic layer is selected from the group consisting of gold and SinXm, where X is selected from the group consisting of oxygen, nitrogen, carbon, and combinations thereof, and xcexa3(n+m) satisfies the valence requirements of Si and X.
In one embodiment, the article further includes a metal layer disposed on a surface of the first substrate, and an inorganic layer disposed on a surface of the second polycarbonate substrate, such that the adhesive composition is in contact with the metal layer of the first substrate and the inorganic layer of the second substrate.
In preferred embodiments, the article is optically clear. In other preferred embodiments, the adhesive composition is optically clear.
In some embodiments, the article is an optical recording medium. The optical recording medium can include data and preferably includes a storage capacity greater than one gigabyte. Examples of suitable optical recording media include DVD, DVD-R, DVD-RW, DVD-RAM, DVR, DVD Audio and DVD hybrids.
In another aspect, the invention features an article that includes: a) a first polycarbonate substrate, b) a second polycarbonate substrate, and c) an adhesive composition disposed between the first polycarbonate substrate and the second polycarbonate substrate such that the first polycarbonate substrate is bonded to the second polycarbonate substrate through the adhesive composition. The adhesive composition includes an adhesive polymer consisting of the reaction product of 1) an N-vinyl containing monomer selected from the group consisting of N-vinyl caprolactam, N-vinyl pyrrolidone, N-vinyl imidazole, and combinations thereof, 2) an acrylic acid ester monomer of a non-tertiary alcohol having an alkyl group comprising 4 to 20 carbon atoms, whose homopolymer has a Tg less than 0xc2x0 C., 3) optionally a monoethylenically unsaturated monomer having from 4 to 20 carbon atoms in the alkyl group, whose homopolymer has a Tg of greater than 10xc2x0 C., 4) optionally a substituted acrylamide, 5) optionally an initiator, 6) optionally a cross-linking agent, and 7) optionally a chain transfer agent.
In other aspects, the invention features an adhesive composition that includes an adhesive polymer consisting of the reaction product of 1) greater than 30 parts by weight N-vinyl caprolactam (based on 100 parts adhesive polymer), 2) an acrylic acid ester monomer of a non-tertiary alcohol having an alkyl group comprising 4 to 20 carbon atoms, whose homopolymer has a Tg less than 0xc2x0 C., 3) optionally a monoethylenically unsaturated monomer having from 4 to 20 carbon atoms in the alkyl group, whose homopolymer has a Tg of greater than 10xc2x0 C., 4) optionally a substituted acrylamide, 5) optionally an initiator, 6) optionally a cross-linking agent; and 7) optionally a chain transfer agent.
In one embodiment, the composition is capable of maintaining a first polycarbonate substrate in fixed relation to a second polycarbonate substrate to form an article that is substantially free of debonding after the article is subjected to Accelerated Aging Test Method II.
In another embodiment, the adhesive composition is capable of bonding a first polycarbonate substrate to a second polycarbonate substrate to form an article that is substantially free of debonding after exposure to 90% relative humidity at 80xc2x0 C. for 16 hours.
In other embodiments, the composition is capable of bonding a first polycarbonate substrate that includes a metal layer disposed on a surface of the polycarbonate, to a second polycarbonate substrate to form an article that is substantially free of corrosion after exposure to 90% relative humidity at 80xc2x0 C. for 16 hours.
In some embodiments, the adhesive composition has a storage modulus of at least about 2xc3x97105 Pa at room temperature.
In one embodiment, the amount of the N-vinyl caprolactam is from about 33 parts by weight to about 50 parts by weight. In other embodiments, the acrylic acid ester monomer is selected from the group consisting of isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, decyl acrylate, lauryl acrylate, hexyl acrylate, butyl acrylate, octadecyl acrylate, and combinations thereof.
In preferred embodiments, the adhesive composition is optically clear. In some embodiments, the adhesive composition is optically clear when disposed between a first polycarbonate substrate and a second polycarbonate substrate and then exposed to 90% relative humidity at 80xc2x0 C. for 16 hours.
In other aspects, the invention features an article that includes a first polyethylene terephthalate substrate comprising silicone disposed on a surface thereof, a second polyethylene terephthalate substrate comprising silicone disposed on a surface thereof, wherein the first substrate is different from the second substrate, and a pressure sensitive adhesive composition according to the above-described adhesive composition disposed between the first substrate and the second substrate.
In a further, aspect the invention features an article that includes a first polycarbonate substrate, a second polycarbonate substrate, and an adhesive composition disposed between the first polycarbonate substrate and the second polycarbonate substrate such that the first polycarbonate substrate is bonded to the second polycarbonate substrate through the adhesive composition, the article being substantially free of debonding after exposure to 85% relative humidity at 80xc2x0 C. for 100 hours. In a preferred embodiment, the first polycarbonate substrate includes data and a metal layer disposed on a surface of the first polycarbonate substrate, and the data is capable of being read according to the DVD Performance Test after exposure to 85% relative humidity at 80xc2x0 C. for 100 hours.
In another embodiment, the article includes a first polycarbonate substrate, a second polycarbonate substrate, and a pressure sensitive adhesive composition disposed between the first polycarbonate substrate and the second polycarbonate substrate such that the first polycarbonate substrate is bonded to the second polycarbonate substrate through the adhesive composition, and the article is substantially free of debonding after exposure to 90% relative humidity at 80xc2x0 C. for 16 hours.
In other aspects, the invention features an article that includes: a) a first polycarbonate substrate, b) a second polycarbonate substrate, and c) an adhesive composition disposed between the first polycarbonate substrate and the second polycarbonate substrate such that the first polycarbonate substrate is bonded to the second polycarbonate substrate through the adhesive composition and the adhesive composition includes an adhesive polymer consisting of the reaction product of 1) a nitrogen containing monomer that is copolymerizable with an acrylic acid ester monomer and whose AlogP value is xe2x89xa61.0, 2) an acrylic acid ester monomer of a non-tertiary alcohol having an alkyl group comprising 4 to 20 carbon atoms, whose homopolymer has a Tg less than 0xc2x0 C., 3) optionally a monoethylenically unsaturated monomer having from 4 to 20 carbon atoms in the alkyl group, whose homopolymer has a Tg of greater than 10xc2x0 C., 4) optionally a substituted acrylamide, 5) optionally an initiator; 6) optionally a cross-linking agent, and 7) optionally a chain transfer agent. In other embodiments, the nitrogen containing monomer has 0.0xe2x89xa6AlogPxe2x89xa61.0. In other embodiments, the acrylic acid ester monomer has an AlogP value greater than 1.0.
In another aspect, the invention features a method of making the above-described polycarbonate article. The method includes contacting the first polycarbonate substrate with the adhesive composition, and contacting the adhesive composition with the second polycarbonate substrate such that the first polycarbonate substrate becomes bonded to the second polycarbonate substrate through the adhesive composition.
The invention provides an adhesive composition that is optically clear and exhibits excellent bond strength to polycarbonate substrates such that it maintains the bond under extreme conditions of elevated relative humidity (about 90%), and elevated temperature (about 80xc2x0 C.). The adhesive composition also provides a bond to polycarbonate of excellent durability. The bond integrity and the optical clarity are also maintained when cooled to room temperature after exposure to such conditions. The adhesive composition is non-corrosive and is particularly well-suited for use in articles that have corrodible surfaces such as articles that include two polycarbonates substrates in which one or both of the substrates has a surface coating such as aluminum. The adhesive composition also exhibits good adhesion to surfaces such as silicon carbide, silicon nitride, and silicon oxide-coated polycarbonate substrates. The adhesive composition can be used in a variety of articles including, e.g., digital versatile discs, e.g., digital video discs, memory switches, vibration dampers, copper circuitry, and multi-layer polycarbonate articles, e.g., windows, as well as in general bonding applications.
Other features of the invention will be apparent from the following description of preferred embodiments thereof, and from the claims.